Production of paper pulp



Aug 7, 1934. P. A. PAULSON 1,969,421

PRODUCTION PAPER PULP Filed Nov. 5. 1932 AdLme Patented Aug. 7, 1934yUNITED STATES PATENT OFFICE This invention relates` to' the productionof paper pulp and particularly to improvements in the sulphite process.

In the manufacture of paper making pulp by the sulphite process thecooking of the wood with the bisulphite acid and steamV usually takesplace in a battery of two or more digesters. 'I'he time allowed for thelling, cooking and emptying a digester is vdivided by the number ofdigesters in use so that the starting of a digester takes place at equalintervals. If, for instance, twelve hours is allowed for a completecycle, and there are four digesters, then a digester is started everythree hours. It thus follows that there are always three digesterscooking when one is being started'.

The cooking takes place 'under a pressurel of from 60 to 80 lbs. persquare inch. The digesters are equipped at the bottom with steam pipesto supply the necessary steam for obtaining the required temperature andpressure.

In common practice )the digesters are also equipped with relief valvesat the top. These valves serve to relieve acid gases and liquor from thedigesters during the cooking process in order that sufficient steam mayfind room in the digesters to raise the charge to the requiredtemperature. 'I'he relief valves are as a rule operated by hand andrequire skillful operators as well as considerable attention if the bestresults are to be obtained.

A principal object of the invention is to provide a method of operationand a system of apparatus which will eliminate the necessity for highlyskilled operators, and will render the various phases of the cookingprocess nearly automatic in their operation.

A further object of the invention is to provide a method of operation inwhich the conditions will be more regular and uniform than in thepreviously known methods.

Another object of Athe invention is to decrease the time' required forthe cooking cycle of operations.

A further object of the invention is to provide for the impregnation ofthe wood chips with acid liquor of the greatest possible strength.

Briefly, the invention comprises the provision of a common relief lineinto which the individual relief valves ofa battery of digesters open,and which is provided with an automatic pressure control device wherebya uniform pressure will always be maintained in the common relief line.The invention also comprises the provision of means for supplying toeach digester a uniform predetermined flow of steam during the rst stageof the cooking period until the desired teniperature'is reached, andthereafter supplying a smaller uniform predetermined flow of steamsufficient to maintain the desired temperature.

'Ihe invention makes it unnecessary for the operator to adjust either ofthe relief valves or steam supply valves. The operator has only to openthe relief valves wide and the automatic pressure 'regulator on thecommon relief main 66 will insure a. uniform pressure on all of thedigesters at the same time.

The provision of a common relief main and of two different steam supplymeans of predetermined capacity makes it possible uniformly andregularly to bring the digesters to full working pressure andtemperature in the shortest possible time.

Furthermore, by buildingy up the pressure in a digester starting thecycle, by means of acid relief gases from other digesters of thebattery, it results that the wood chips vare impregnated with acidliquid of the highest possible strength and at the maximum'pressure,since the attaining of the necessary pressureis not dependent upon thesupplying' of steam to the digester whichhas the effect of weakening thestrength of the acid in proportion as it builds up the temperature.

In ordinary practice it takes from two to six hours to bring a digesterto full working pressure. With my method of the invention it can be donein from ten to fifteen minutes. When the digester has been filled withchips and acid, the operator will open the relief valve and the pressurefrom the other digesters already relieving will enter the newly filleddigester at the top and bring up the pressure on it almost immediately.

The steam entering the bottom of the digester is madeto go through anozzle or orifice of a predetermined size that will bring the contentsof the digester to the desired temperature in a specified time. Asmaller nozzle or orifice that will just maintain the correcttemperature is then used until the cook is finished.

The invention will be more particularly described for the purpose ofillustration with reference to the accompanying drawing which is adiagrammatic representation of a system of ap- -paratus embodying theprinciples of the invention.

The apparatus shown comprises a battery of three digesters ,1, eachhaving an acid supply line 2, and a discharge line 3 leading to theblowpit. Each digester is provided at the top with a relief line andvalve 4 leading into a com- 110 mon relief main 5, leading to an acidreclaiming system, not shown. In therelief main between the battery ofdigesters and the acid reclaiming system is located an automaticpressure control valve 6, adjusted to maintain in the relief main thepressure necessary for proper cooking.

Each digester is supplied with steam inlets '7 at the bottom. The steaminlets are'fed from a source of steam 8, through an arrangement whichpermits the steam to be supplied either through a small orifice ofpredetermined capacity S), or a larger orifice of predeterminedcapacitylO.

A manhole opening for admitting the wood chips into the digester andcover 1l are provided oneach digester. l

'I'he method of operation after the establishment of a regular cycle maybe as follows: After an emptied digester is filled with Wood chips andacid andthe covervll has been bolted on, the relief valve 4, which hasbeen closed during ythe emptying and filling operations, is opened Wide.Acid gases and liquor from the other digesters which are at this time inthe cooking stage enter the newly filled digester through valve 4 andbring it up to full pressure almost immediately. It is to be noted thatthe operator does not have to manipulate orv adjust valve 4 for anypurpose until it is closed at the vend of the cooking operation.

After relief valve 4 is opened, the operator opens the valve supplyingsteam to the digester through the larger orifice l0, the size of whichis calculated to supply sufficient steam to bring the contents of 'thedigester to the desired maximum temperature in. a predetermined time.After the maximum temperature is reached the valve supplying steamthrough orifice 10 is closed and that supplying steam through thesmaller orifice 9 is opened. The size -of the smaller orice iscalculated to admit suflicient steam to maintain the contents of thedigester at the desired maximum temperature.

I claim: y

1. A method of making wood pulp by the sulphite process which comprisesfilling a digester forming one of a battery of digesters with Wood chipsand bisulpliite liquor, bringing the upper portion of said digester intofree communication with the upper portions of the other digesters of thebattery which are undergoing cooking, passing steam into said digesterat a predetermined constant rate until the contents of the digesterreach the desired maximum temperature, and thereafter passing steam intosaid digester at a lower predetermined constant rate adapted to maintainthe contents of the digester at the .desired maximum temperature.

2. Apparatus for the manufacture of Wood pulp by the sulphite processincluding a battery of digesters, a common header, means for bringingthe upper portion of each of said digesters into communication with saidcommon header for the passage of gases and liquids between saiddigesters, and means for maintaining a predetermined maximum pressure onsaid common header.

3. Apparatus for the manufacture of Wood pulp by the sulphite processincluding a battery of digesters, means for supplying steam to saiddigesters, said means including a xed orifice of predetermined sizeadapted to supply steam at a rate sufficient to bring the contents ofthe digesters to the desired temperature in a predetermined period oftime, and a second fixed orifice of predetermined sizeadapted to supplysteam at a rate sufficient to maintain the contents of the digesters atthe desired temperature, a common header, means for bringing the upperportion of each of said digesters into communication with said commonheader for the passage of gases and liquids between said digesters, andmeans for maintaining a predetermined maximum pressure on said commonheader.

4. A method of making wood pulp by the sulphite process which comprisesfilling a digester forming one of a battery 0f digesters with wood chipsand bisulphite liquor, bringing the upper portion of said digester intofree communication with the upper portions of the other digesters of thebattery which are undergoing cooking' and thereafter supplying steam tosaid digester while maintaining said free communication throughout thecooking period whereby all of the digesters undergoing cooking aremaintained at the same pressure.y

5. In the production of wood pulp by the suli

